Network server layer providing disjoint channels in response to client-layer disjoint path requests

ABSTRACT

In one embodiment, a network server layer provides disjoint channels in response to client-layer disjoint path requests. For example, the network layer can be an optical network, and the client layer may be a packet switching layer (e.g., label switching, Internet Protocol). In one embodiment, a server-layer node receives a client-layer disjoint path request to provide a server-layer channel through a server-layer network. The client-layer disjoint path request includes an identifier corresponding to an existing client-layer path that traverses a current channel through the server-layer network that does not include the server-layer node. The server-layer network determines a particular channel through the server-layer network that is disjoint to the current channel based on route information of the current channel, and then signaling is performed within the server-layer network to establish the particular channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/801,667, filed Mar. 13, 2013, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to communicating information,such as in packets, in a multi-layer communications network.

BACKGROUND

The communications industry is rapidly changing to adjust to emergingtechnologies and ever increasing customer demand. This customer demandfor new applications and increased performance of existing applicationsis driving communications network and system providers to employnetworks and systems having greater speed and capacity (e.g., greaterbandwidth). In trying to achieve these goals, a common approach taken bymany communications providers is to use packet switching technology.

Reliably and efficiently communicating information in a network isimportant. Different techniques may be employed in a network tocommunicate information in a network when the topology of the networkchanges and/or when communications resources become available.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended claims set forth the features of one or more embodimentswith particularity. The embodiment(s), together with its advantages, maybe best understood from the following detailed description taken inconjunction with the accompanying drawings of which:

FIGS. 1A-C illustrate a network operating according to one embodiment;

FIG. 2A illustrates a packet switching device according to oneembodiment;

FIG. 2B illustrates an apparatus (e.g., optical node) according to oneembodiment;

FIG. 3 illustrates a process according to one embodiment; and

FIG. 4 illustrates a process performed on a node-by-node basis accordingto one embodiment.

DESCRIPTION OF EXAMPLE EMBODIMENTS 1. Overview

Disclosed are, inter alia, methods, apparatus, computer-storage media,mechanisms, and means associated with a network server layer providingdisjoint channels in response to client-layer disjoint path requests.

In one embodiment, a server-layer node receives a client-layer disjointpath request to provide a server-layer channel through a server-layernetwork. The client-layer disjoint path request includes an identifiercorresponding to an existing client-layer path that traverses a currentchannel through the server-layer network that does not include theserver-layer node. The server-layer network determines a particularchannel through the server-layer network that is disjoint to the currentchannel based on route information of the current channel, and thensignaling is performed within the server-layer network to establish theparticular channel.

In one embodiment, in response to receiving a disjoint label switchedpath (LSP) request for a new LSP to be carried through an opticalnetwork over a new channel that is disjoint from an existing channelcarrying a current LSP, an optical node determines the new channelthrough the optical network that is disjoint to the current channelbased on route information through the optical network related to thecurrent channel, wherein the existing channel is not terminated on theoptical node. Signaling is performed in the optical network to establishthe particular channel.

2. Description

Disclosed are, inter alia, methods, apparatus, computer-storage media,mechanisms, and means associated with a network server layer providingdisjoint channels in response to client-layer disjoint path requests.Embodiments described herein include various elements and limitations,with no one element or limitation contemplated as being a criticalelement or limitation. Each of the claims individually recites an aspectof the embodiment in its entirety. Moreover, some embodiments describedmay include, but are not limited to, inter alia, systems, networks,integrated circuit chips, embedded processors, ASICs, methods, andcomputer-readable media containing instructions. One or multiplesystems, devices, components, etc., may comprise one or moreembodiments, which may include some elements or limitations of a claimbeing performed by the same or different systems, devices, components,etc. A processing element may be a general processor, task-specificprocessor, a core of one or more processors, or other co-located,resource-sharing implementation for performing the correspondingprocessing. The embodiments described hereinafter embody various aspectsand configurations, with the figures illustrating exemplary andnon-limiting configurations. Computer-readable media and means forperforming methods and processing block operations (e.g., a processorand memory or other apparatus configured to perform such operations) aredisclosed and are in keeping with the extensible scope of theembodiments. The term “apparatus” is used consistently herein with itscommon definition of an appliance or device.

The steps, connections, and processing of signals and informationillustrated in the figures, including, but not limited to, any block andflow diagrams and message sequence charts, may typically be performed inthe same or in a different serial or parallel ordering and/or bydifferent components and/or processes, threads, etc., and/or overdifferent connections and be combined with other functions in otherembodiments, unless this disables the embodiment or a sequence isexplicitly or implicitly required (e.g., for a sequence of reading thevalue, processing said read value—the value is obtained prior toprocessing it, although some of the associated processing may beperformed prior to, concurrently with, and/or after the read operation).Also, nothing described or referenced in this document is admitted asprior art to this application unless explicitly so stated.

The term “one embodiment” is used herein to reference a particularembodiment, wherein each reference to “one embodiment” may refer to adifferent embodiment, and the use of the term repeatedly herein indescribing associated features, elements and/or limitations does notestablish a cumulative set of associated features, elements and/orlimitations that each and every embodiment includes, although anembodiment typically may include all these features, elements and/orlimitations. In addition, the terms “first,” “second,” etc., aretypically used herein to denote different units (e.g., a first element,a second element). The use of these terms herein does not necessarilyconnote an ordering such as one unit or event occurring or coming beforeanother, but rather provides a mechanism to distinguish betweenparticular units. Moreover, the phrases “based on x” and “in response tox” are used to indicate a minimum set of items “x” from which somethingis derived or caused, wherein “x” is extensible and does not necessarilydescribe a complete list of items on which the operation is performed,etc. Additionally, the phrase “coupled to” is used to indicate somelevel of direct or indirect connection between two elements or devices,with the coupling device or devices modifying or not modifying thecoupled signal or communicated information. Moreover, the term “or” isused herein to identify a selection of one or more, including all, ofthe conjunctive items. Additionally, the transitional term “comprising,”which is synonymous with “including,” “containing,” or “characterizedby,” is inclusive or open-ended and does not exclude additional,unrecited elements or method steps. Finally, the term “particularmachine,” when recited in a method claim for performing steps, refers toa particular machine within the 35 USC §101 machine statutory class.

As used herein, a server-layer Shared Risk Link Group (SRLG) refers to aset of one or more things in the server network that will fail together,with these things being links, devices, nodes, etc. For example, an SRLGmay be a device, such as a switch, repeater, regenerator, link, etc. Twolinks that traverse a same single point of failure (e.g., arewavelengths within a same fiber, are in different fibers that areco-located such as within a same conduit, or run under a same buildingsuch as they would both fail upon building collapse).

One embodiment includes a method, comprising: receiving, by aserver-layer node, a client-layer disjoint path request to provide aserver-layer channel through a server-layer network, with theclient-layer disjoint path request including an identifier correspondingto an existing client-layer path that traverses a current channelthrough the server-layer network that does not include the server-layernode; determining, by the server-layer network, a particular channelthrough the server-layer network that is disjoint to the current channelbased on route information of the current channel; and signaling withinthe server-layer network to establish the particular channel.

One embodiment includes requesting and receiving by the server-layernode from a second server-layer node in the server-layer network saidroute information of the current channel. In one embodiment, the currentchannel is terminated at the server-layer by the second server-layernode. In one embodiment, the identifier is a channel identifierincluding an identification of the second server-layer node. In oneembodiment, the identifier is a channel identifier including anidentification of the second server-layer node. One embodiment includes:subsequent to the particular channel being established, sending by theserver-layer node one or more messages to the second server-layer nodeidentification information concerning the particular channel to beassociated by the second-layer node with the current channel. In oneembodiment, said one or more messages are unicast messages between theserver-layer node and the second server-layer node.

In one embodiment, said determining, by the server-layer network, theparticular channel through the server-layer network that is disjoint tothe current channel based on route information of the current channel isperformed by the server-layer node. In one embodiment, said determining,by the server-layer network, the particular channel through theserver-layer network that is disjoint to the current channel based onroute information of the current channel is performed on a node-by-nodebasis within the server-layer network. One embodiment includes:receiving, by the server-layer node, one or more server-layer networkroute advertisement messages communicating that the current channel isterminated at the server-layer by the second server-layer node.

One embodiment includes: receiving, by the server-layer node, one ormore server-layer network route advertisement messages communicatingsaid route information of the current channel. One embodiment includes:maintaining, by the server-layer node, a server-layer database includingsaid route information of the current channel; and wherein saiddetermining the particular channel includes retrieving said routeinformation from the server-layer database. One embodiment includes:subsequent to the particular channel being established, sending by theserver-layer node one or more server-layer advertisement messages to bereceived by the second server-layer node and including identificationinformation concerning the particular channel to be associated with thecurrent channel.

In one embodiment, the server-layer is an optical network layer. In oneembodiment, the client-layer is Layer 3. In one embodiment, theclient-layer path is a label switched path; and wherein the client-layerdisjoint path request is for a second label switched path.

One embodiment includes a method, comprising: in response to receiving adisjoint label switched path (LSP) request for a new LSP to be carriedthrough an optical network over a new channel that is disjoint from anexisting channel carrying a current LSP, an optical node determining thenew channel through the optical network that is disjoint to the currentchannel based on route information through the optical network relatedto the current channel, wherein the existing channel is not terminatedon the optical node; and signaling in the optical network to establishthe particular channel.

In one embodiment, the current channel is terminated in the opticalnetwork by a second optical node; and wherein the method includes:requesting, by the optical node, said route information from the secondoptical node, and subsequently receiving, by the optical node, saidroute information. One embodiment includes: receiving, by the opticalnode, one or more optical network route advertisement messagescommunicating said route information of the current channel.

One embodiment includes an optical node, comprising: one or moreprocessing elements; memory; and a plurality of optical interfacesconfigured to send and receive packets. In one embodiment, said one ormore processing elements are configured to perform operations,including: in response to receiving a disjoint label switched path (LSP)request for a new LSP to be carried through an optical network over anew channel that is disjoint from an existing channel carrying a currentLSP, the optical node determining the new channel through the opticalnetwork that is disjoint to the current channel based on routeinformation through the optical network related to the current channel,wherein the existing channel is not terminated on the optical node; andsignaling in the optical network to establish the particular channel

In one embodiment, the current channel is terminated in the opticalnetwork by a second optical node; and wherein the method includes:requesting, by the optical node, said route information from the secondoptical node, and subsequently receiving, by the optical node, saidroute information.

Expressly turning to the figures, FIG. 1A illustrates a network 100operating according to one embodiment. Shown is a server-layer network100 (e.g., optical network, non-packet switched network) includingoptical nodes/devices 111-117. The use of the phrase “nodes/devices” isto indicate that some of these appliances may include a processingcapability (e.g., an optical node) or an optical device (e.g., opticalregenerators, cross-connects, transponders). A client-layer network isshown including packet switching devices 101-104.

As illustrated in FIG. 1A, a client-layer path (in this example a labelswitched path or LSP) is established over an (end-to-end) opticalchannel 119 through optical network 110, that goes through opticalnodes/devices 111, 112 and 113. This optical channel is terminated onoptical nodes 111 and 113. In one embodiment, optical node 111 initiatedthe establishment of this optical channel 119; thus, it has a list oflinks and nodes (sometimes referred to as an explicit route object orERO) in the optical network that optical channel 119 traverses.

In one embodiment and turning to FIG. 1B, packet switching device 103(e.g., a client device) requests that optical node 114 establish anoptical channel through optical network 110 to carry a particular labelswitched path (LSP) that is disjoint from LSP 119 that traverses opticalnetwork 110. As LSP neither traverse nor terminates on optical node 114,optical node 114 needs to acquire information concerning the end-to-endchannel through optical network 110 taken by LSP 115.

In one embodiment, optical node 114 receives a channel identifiercorresponding to LSP as part of the disjoint path request from packetswitching device 103, which learned of this information as theclient-layer network floods this information using a routing or othernetwork information distribution protocol. In one embodiment, thechannel identifier includes information such as an identification of theLSP, an address of the originating server-layer node (e.g., that nodewill have the complete path information), and a server-layer channelidentifier identifying that channel through the server-layer network. Inone embodiment, the channel identifier includes an address of the otherend node of the path through the server network (e.g., the end node thatis not the originating server-layer node). Based on this channelidentifier, optical node 114 requests and receives the ERO of theoptical channel that carries LSP 115. Therefore, optical node 114 nowhas a list of links, nodes, devices, shared link risk groups, etc. thatit must avoid. In one embodiment, rather than having to request the ERO,when a server-layer channel is created, the ERO of a new channel isflooded by the originating server-layer node through the server network,and server-layer nodes maintain this information. In one embodiment, achannel identifier is flooded by the originating server-layer nodethrough the server network in addition to, or in place of, the ERO.

After acquiring the ERO (e.g., after requesting or retrieving from adata structure), optical node 114 determines a new path (151) throughoptical network that is disjoint from the optical channel 115, with newpath 151 shown in FIG. 1B to traverse optical nodes/devices 114, 115,116, and 117.

FIG. 1C illustrates one or more processes performed in one embodiment,such as in conjunction with network 100 of FIGS. 1A and 1B. First, acurrent channel through the optical network is established by opticalnode 111, including by signaling (161) through the optical network.Client-layer traffic is then transported across this client-layer pathover this current optical channel. Packet switching device 103 receivesinformation concerning the topology of this channel in the client-layernetwork, as well as limited typically information (e.g., a channelidentifier) that includes an address of a server-layer node associatedwith the server-layer channel (e.g., an Internet Protocol (IP) addressof the originating server-layer node).

Subsequent to the establishment of the current channel, packet switchingdevice 103 communicates (171) a disjoint path request specifying thechannel identifier of the current client-layer path (e.g., LSP). In thisembodiment, this channel identifier includes: an identification of theLSP, a specification of an IP address of originating optical node 111,and an identification of the optical channel that carries the LSP.

Optical node 114, based on this request and the received channelidentifier, requests (172) and receives (173) from the current channel'soriginating optical node 111 current channel information (e.g., ERO orsome other specification of resources and/or SRLG's associatedtherewith). Optical node 114 determines (174) a new channel through thenetwork that is disjoint from the current channel (e.g., does not usethe same resources and/or SRLG's associated therewith). Optical node 114signals (175) to the optical network to establish this new channel.Optical node 114 sends (e.g., unicasts/sends addressed to) optical node111 information (e.g., a channel identifier) of the disjoint new opticalchannel. Optical node 111 associates (181) this disjoint property of thenew optical channel with that of the current optical channel, as anyreconfiguration or reoptimization of the current optical channel shouldmaintain the disjoint property with the new optical channel.

One embodiment of a packet switching device 200 is illustrated in FIG.2A. As shown, packet switching device 200 includes multiple line cards201 and 205, each with one or more network interfaces for sending andreceiving packets over communications links (e.g., over optical links toan optical network), and with one or more processing elements that areused in one embodiment associated with a network server layer providingdisjoint channels in response to client-layer disjoint path requests.Packet switching device 200 also has a control plane with one or moreprocessing elements 202 for managing the control plane and/or controlplane processing of packets associated with a network server layerproviding disjoint channels in response to client-layer disjoint pathrequests. Packet switching device 200 also includes other cards 204(e.g., service cards, blades) which include processing elements that areused in one embodiment to process packets associated with a networkserver layer providing disjoint channels in response to client-layerdisjoint path requests, and some communication mechanism 203 (e.g., bus,switching fabric, matrix) for allowing its different entities 201, 202,204 and 205 to communicate.

FIG. 2B is a block diagram of an apparatus 220 used in one embodimentassociated with a network server layer providing disjoint channels inresponse to client-layer disjoint path requests. In one embodiment,apparatus 220 performs one or more processes, or portions thereof,corresponding to one of the flow diagrams illustrated or otherwisedescribed herein, and/or illustrated in another diagram or otherwisedescribed herein.

In one embodiment, apparatus 220 includes one or more processingelement(s) 221, memory 222, storage device(s) 223, specializedcomponent(s) 225 (e.g. optimized hardware such as for performing lookupand/or packet processing operations, etc.), and optical and/orelectrical interface(s) 227 for communicating information (e.g., sendingand receiving packets, user-interfaces, displaying information, etc.),which are typically communicatively coupled via one or morecommunications mechanisms 229, with the communications paths typicallytailored to meet the needs of a particular application.

Various embodiments of apparatus 220 may include more or fewer elements.The operation of apparatus 220 is typically controlled by processingelement(s) 221 using memory 222 and storage device(s) 223 to perform oneor more tasks or processes. Memory 222 is one type ofcomputer-readable/computer-storage medium, and typically comprisesrandom access memory (RAM), read only memory (ROM), flash memory,integrated circuits, and/or other memory components. Memory 222typically stores computer-executable instructions to be executed byprocessing element(s) 221 and/or data which is manipulated by processingelement(s) 221 for implementing functionality in accordance with anembodiment. Storage device(s) 223 are another type of computer-readablemedium, and typically comprise solid state storage media, disk drives,diskettes, networked services, tape drives, and other storage devices.Storage device(s) 223 typically store computer-executable instructionsto be executed by processing element(s) 221 and/or data which ismanipulated by processing element(s) 221 for implementing functionalityin accordance with an embodiment.

FIG. 3 illustrates a process performed in one embodiment. Processingbegins with process block 300. In process block 302, a currentclient-layer path (e.g., Layer-3, IP, LSP) between two client-layerdevices is established, including using a current circuit through aserver network (e.g., optical network) between first and second opticalnodes. In process block 304, a third client device receives floodedclient-layer information concerning the current client-layer path (e.g.,including a circuit identifier relating the client-layer path to theserver-layer circuit).

In process block 306, the third client device requests, from a differentserver node, a new channel through the server network for a newclient-layer path disjoint from the current path through the servernetwork identified by the current path's channel identifier.

As determined in process block 307, if the new server node has theinformation (e.g., ERO) about the resources and/or SRLGs associated withthe current path (e.g., they were flooded through the network after thecircuit was established and maintained in a data structure in the newserver node), then processing proceeds to process block 310. Otherwise,this information is acquired by the new server node by requesting itfrom the server node identified in the current path's channelidentifier.

Next, in process block 310, the new server node determines (e.g., itselfor possibly in communication with a network management or other device)a new disjoint circuit through the server network. In process block 312,the new server node signals to the server network to establish the newcircuit, disjoint from the current circuit. In process block 314, achannel identifier associated with the new server-layer circuit andclient-layer path is either flooded through the server network orunicast and received by the server node identified in the current path'schannel identifier, so that it can update its data structure that thecurrent circuit should be disjoint from the new circuit (e.g., in caseof reoptimization). Processing of the flow diagram of FIG. 3 is completeas indicated by process block 319.

FIG. 4 illustrates a process performed on a node-by-node basis accordingto one embodiment. In one embodiment, the processing of FIG. 4corresponds to the processing of process blocks 310-312 of FIG. 3.

Processing begins with process block 400. In process block 402, aningress server node determines a new circuit through the server-layernetwork corresponding to a received request (e.g., such as, but notlimited to, in process block 306-308 of FIG. 3). As determined inprocess block 405, if a circuit (e.g., an optical light path between aningress optical node and an egress optical node through an opticalnetwork in one embodiment) is found, then in process block 410, the nextnode along this circuit is signaled with the current client-layer pathinformation. As determined in process block 413, if this path is stilldisjoint from the current client-layer path (e.g., disjoint to a circuitportion of the server-layer network on which the current path residesdetermined based on comparing the received current client-layer pathinformation with a data structure including information about currentpaths for which it is currently providing resources), then processingproceeds to process block 417. If the current node is not the egressserver-layer node, then processing returns to process block 410 tosignal the next node (e.g., to continue the determination, by theserver-layer network, the channel through the server-layer network on anode-by-node basis). Otherwise, as determined in process block 417 thatthe current node is the egress server-layer node, then in process block418, the disjoint circuit is established through the server-layernetwork (e.g., using Resource Reservation Protocol (RSVP) signaling inthe reverse direction along the path taken through the server-layernetwork); and processing of the flow diagram of FIG. 4 is complete asindicated by process block 419.

Otherwise, as determined in process block 413, the circuit is notdisjoint to the current path (e.g., not disjoint to a circuit portion ofthe server-layer network on which the current path resides determinedbased on comparing the received current client-layer path informationwith a data structure including information about current paths forwhich it is currently providing resources). Then, in process block 414,the ingress server-layer node is signaled that that circuit is notdisjoint. The server-layer node prunes non-disjoint resources (e.g.,SRLG, links and/or the server-layer node that determined the circuit wasnot disjoint) from the space of network resources on which it isdetermining the circuit; and processing returns to process block 402.

If in process block 405, a determination is made that there is nodisjoint circuit through the server-layer network, then in process block406, failure is signaled (e.g., to the requesting client-layer nodeand/or to an operations/network management system indicating analarm/warning/informational message). Processing of the flow diagram ofFIG. 4 is complete as indicated by process block 409.

In view of the many possible embodiments to which the principles of thedisclosure may be applied, it will be appreciated that the embodimentsand aspects thereof described herein with respect to thedrawings/figures are only illustrative and should not be taken aslimiting the scope of the disclosure. For example, and as would beapparent to one skilled in the art, many of the process block operationscan be re-ordered to be performed before, after, or substantiallyconcurrent with other operations. Also, many different forms of datastructures could be used in various embodiments. The disclosure asdescribed herein contemplates all such embodiments as may come withinthe scope of the following claims and equivalents thereof.

What is claimed is:
 1. A method, comprising: receiving, by anoptical-layer ingress server of an optical network, a client-layerdisjoint path request to provide an optical circuit through the opticalnetwork that is disjoint to a particular existing client-layer path thattraverses an existing optical circuit through the optical network;initiating, by the optical-layer ingress server, a first new circuitthrough the optical network to be disjoint to the existing opticalcircuit through the optical network; determining, by a first opticalnode along the first new circuit, that the first new circuit is notdisjoint to the existing optical circuit; sending, to the optical-layeringress server by the first optical node, a first signal identifyingthat the first new circuit is not disjoint to the existing opticalcircuit; receiving, by the optical-layer ingress server, the firstsignal; and in response to said receiving the first signal, initiating,by the optical-layer ingress server, a second new circuit through theoptical network to be disjoint to the existing optical circuit throughthe optical network.
 2. The method of claim 1, wherein the second newcircuit is established and is disjoint from the existing opticalcircuit.
 3. The method of claim 2, comprising: determining, by a secondoptical node along the second new circuit, that the second new circuitis disjoint to the existing optical circuit.
 4. The method of claim 2,comprising in response to determining, by a second optical node alongthe second new circuit, that the second new circuit is disjoint to theexisting optical circuit: signaling to a third optical node along thesecond new circuit in establishing the second new circuit.
 5. The methodof claim 2, comprising: in response to receiving the first signal,pruning one or more non-disjoint links associated with the first newcircuit or one or more non-disjoint nodes associated with the first newcircuit from a search space of possible optical paths through theoptical network that are disjoint to the existing optical circuitthrough the optical network.
 6. The method of claim 5, comprising:determining, by the optical-layer ingress server, each of the first newcircuit and the second new circuit based on a respective current stateof the search space.
 7. The method of claim 1, wherein said determiningthat the first new circuit is not disjoint to the existing opticalcircuit is performed as during the establishment phase of the first newcircuit.
 8. The method of claim 1, comprising: determining, by a secondoptical node along the second new circuit, that the second new circuitis not disjoint to the existing optical circuit; sending, to theoptical-layer ingress server by the second optical node, a second signalidentifying that the second new circuit is not disjoint to the existingoptical circuit; receiving, by the optical-layer ingress server, thesecond signal; and in response to said receiving the second signal,initiating, by the optical-layer ingress server, a third new circuitthrough the optical network to be disjoint to the existing opticalcircuit through the optical network.
 9. The method of claim 8, whereinthe third new circuit is established and is disjoint from the existingoptical circuit.
 10. The method of claim 1, comprising: in response toreceiving the first signal, pruning one or more non-disjoint linksassociated with the first new circuit or one or more non-disjoint nodesassociated with the first new circuit from a search space of possibleoptical paths through the optical network that are disjoint to theexisting optical circuit through the optical network.
 11. The method ofclaim 10, comprising: determining, by the optical-layer ingress server,each of the first new circuit and the second new circuit based on arespective current state of the search space.
 12. The method of claim 1,wherein the client-layer disjoint path request is for a label switchedpath.
 13. A method, comprising: receiving, by an optical-layer ingressserver of an optical network, a client-layer disjoint path request toprovide an optical circuit through the optical network that is disjointto a particular existing client-layer path that traverses an existingoptical circuit through the optical network; initiating, by theoptical-layer ingress server, a first new circuit through the opticalnetwork to be disjoint to the existing optical circuit through theoptical network; receiving, by the optical-layer ingress server, asignal identifying that the first new circuit was not disjoint to theexisting optical circuit; and in response to said receiving the signal,initiating, by the optical-layer ingress server, a second new circuitthrough the optical network to be disjoint to the existing opticalcircuit through the optical network.
 14. The method of claim 13,comprising: in response to receiving the signal identifying that thefirst new circuit was not disjoint to the existing optical circuit,pruning one or more non-disjoint links or one or more non-disjoint nodesfrom a search space of possible optical paths through the opticalnetwork that are disjoint to the existing optical circuit through theoptical network.
 15. The method of claim 14, comprising: determining, bythe optical-layer ingress server, each of the first and second newcircuits based on a respective current state of the search space.
 16. Anoptical-layer ingress server, comprising: one or more processingelements; memory; and a plurality of optical interfaces that send andreceive packets; wherein the optical-layer ingress server performsoperations, including in response to a client-layer disjoint pathrequest to provide an optical circuit through the optical network thatis disjoint to a particular existing client-layer path that traverses anexisting optical circuit through the optical network: initiating a firstnew circuit through the optical network to be disjoint to the existingoptical circuit through the optical network; receiving a signalidentifying that the first new circuit was not disjoint to the existingoptical circuit; and in response to said receiving the signal,initiating a second new circuit through the optical network to bedisjoint to the existing optical circuit through the optical network.17. The optical-layer ingress server of claim 16, where said operationsinclude: in response to receiving the signal identifying that the firstnew circuit was not disjoint to the existing optical circuit, pruningone or more non-disjoint links or one or more non-disjoint nodes from asearch space of possible optical paths through the optical network thatare disjoint to the existing optical circuit through the opticalnetwork.
 18. The optical-layer ingress server of claim 17, where saidoperations include determining each of the first and second new circuitsbased on a respective current state of the search space.
 19. A method,comprising: receiving, by an optical node, a client-layer disjoint pathrequest to provide an optical circuit through an optical network, withthe client-layer disjoint path request including an identifiercorresponding to an existing client-layer path that traverses a currentoptical circuit through the optical network; receiving by the opticalnode from a second optical node in the optical network route informationof the current optical circuit; determining, by the optical node, aparticular optical circuit through the optical network that is disjointto the current circuit based on said received route information of thecurrent circuit; and signaling within the optical network to establishthe particular circuit.
 20. The method of claim 19, comprising signalingwithin the optical network information concerning the establishment ofthe particular circuit.